Re: more on delete from join
Date: Wed, 26 Aug 2009 14:35:44 -0700 (PDT)
On Aug 26, 2:14 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> Tegiri Nenashi wrote:
> > On Aug 26, 1:03 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> >> I meant "AND" as the logical connective, not shorthand for relational
> >> "<AND>". "R AND A" stands for a logical conjunction of propositions,
> >> each proposition having been concluded to be true.
> > Stop right there. You were writing R UNION A, so R and A are relations
> > (or predicates) and not propositions. ...
> Okay, I'll stop right there and be even more precise, relations are not
> predicates, they are representations of predicates.
Can you express the difference formally? I would insist relations and predicates being the same thing. One can distinguish finite predicates, and infinite predicates: countable or uncountable ones. If you call finite predicate a relation, then I'm OK with this distinction.
> Actually, it is
> precision that enables the conclusion from two different
> representations, because they are both representations of the same
> things - propositions.
Propositions and predicates are not the same thing. Propositions are studied in Propositional Calculus, while Predicate Calculus introduces new things: predicates. Predicate has a number of unbound variables. Only after you apply quantifiers to a predicate, so that all variables are bound, the expression evaluates to a proposition. Received on Wed Aug 26 2009 - 23:35:44 CEST